Soft tissue is the most abundant tissue in the human body. Most soft tissue is collagen--over 90% of the organic matter in tendons and ligaments is collagen. The connective tissue in joints is comprised of soft tissue, generally collagen tissue. When soft tissue in a joint is damaged, the healing process is often long and painful.
Well-known methods for addressing the treatment of soft tissue in injured joints include strengthening exercises, open surgery, and arthroscopic techniques. Using current treatments, many people with injured joints suffer from prolonged pain, loss of motion, nerve injury, and some develop osteoarthritis. The soft tissue in many injured joints never heals enough to return the damaged joint to its full range of function.
It is known in the art that thermal energy applied to soft tissue, such as collagen tissue, in joints may alter or manipulate the tissue to provide a therapeutic response during thermal therapy. In particular, applying controlled thermal energy to soft tissue in an injured joint can cause the collagenous tissue to shrink, thereby tightening unstable joints.
Medical probes for the rehabilitative thermal treatment of soft tissues are known in the art. Examples of these probes include laser probes and RF heated probes. While these tools meet the basic need for rehabilitative thermal treatment of soft tissues, such as collagen tissues, many suffer from temperature over-shoot and under-shoot fluctuation causing unpredictable results in the thermal alteration.
One medical probe in U.S. Pat. No. 5,458,596 to Lax, et al., discloses examples of a probe with a proximal and distal end that employs heat for the controlled contraction of soft tissue. However, a potential drawback of many prior art probes is that the probe's temperature can become unstable when heat from the probe is dissipated into the mass of the treated tissue. This situation can be a particular problem when treating dense tissue; dense tissue acts as a heat sink thereby requiring additional energy input to maintain the desired temperature. The application of additional energy in an attempt to compensate for the heat sink effect can cause an underdamped effect before settling out at the correct temperature.
In general, a system is overdamped when its damping factor is greater than one and has a slow response time. A system is critically damped when its damping factor is exactly one. A system is underdamped when its damping factor is less than one. In an underdamped system, "ringing" is a problem because it can cause the momentary application of temperatures that are too high for the safe heating of soft tissue. When this occurs, damage to the soft tissue may result from charring, ablation or the introduction of unwanted and harmful effects on the soft tissue causing injury.
Typically, the medical probes are attached to a controller to control the power output of the probe based on an actual temperature measurement from a temperature sensor such as a thermocouple in the probe and a set predetermined target temperature. The controller is part of a system that includes circuitry to monitor sensed temperature from the temperature sensor. Temperature-controlled probes are designed to provide precise coagulation to eliminate damage, charring, and bubbles. Different size probes with various configurations are available to treat various joint sizes including the shoulder, knee, ankle, wrist and the elbow.
Precise temperature control of the system in which the probes are used is required during various types of thermal therapy of soft tissue. For example, during hyperthermia which is defined as the treatment of diseased soft tissue by raising the bodily temperature by physical means, some prior art probes have difficulty in providing smooth and consistent heating because the preferred materials for the energy delivery electrodes are highly thermally responsive materials. Such materials generally do not retain large amounts of heat energy. At initiation, the controller rapidly heats the probe to achieve the target temperature which can result in an overshoot problem. During application, contact with large tissue masses tends to cause underdamped fluctuations in the probe temperature due to vast differences in the temperature of the surrounding tissue mass. Likewise, one skilled in the art will appreciate that similar problems may occur during a desired reduction in the soft tissue temperature.
In addition, different probes have different operating characteristics. Applications using larger probes typically need relatively large amounts of power to reach and maintain the desired temperature. Applications using smaller probes, such as a spine probe, need a well-controlled and precise stable temperature. However, the typical controller uses the same method to control the power output of all the different probes and does not change its control process in response to different types of probes further contributing to overshoot and undershoot problems.
Therefore, a method and apparatus are needed that allows the controller to change operation in response to the type of probe attached. This method and apparatus should also reduce temperature overshoot and oscillation while initiating and applying treatment.